Coating composition and coating film

Abstract

To provide a coating composition which can form a coated body having excellent coating film drying properties, excellent blocking resistance and excellent water resistance when applying a water-based coating in a factory. [Solution] This is a paint composition containing water, an organic solvent, a pigment, and a resin, wherein the pigment volume concentration (PVC) is within the range of 0.1 to 35%, and the resin has at least one spectral peak in a temperature change curve of loss tangent (tanδ) measured at a measurement frequency of 1 Hz using a solid viscoelasticity measuring device based on JIS K7244-4, in the range of 45°C to 180°C.

Description

[Technical Field]

[0001] The present invention relates to a coating composition and a coating film obtained from the coating composition, and in particular to a coating composition that can form a coated body that has excellent coating film drying properties, excellent blocking resistance, and excellent water resistance when applying an aqueous coating in a factory. [Background technology]

[0002] A variety of coating compositions have been proposed for use on metal substrates, but from the viewpoint of reducing the environmental load, aqueous coating compositions are desired, and various proposals have been made.

[0003] Japanese Patent Laid-Open Publication No. 7-300574 (Patent Document 1) describes an invention relating to an aqueous coating composition containing a water-based acrylic-modified alkyd resin and a water-based acrylic-modified epoxy resin as binders. This invention relates to an aqueous coating composition that is water-based and has ultra-fast drying properties and is suitable for use in rust prevention on lightweight steel. The invention described in Patent Document 1 provides a coating film with excellent rust prevention properties, including roll-touch film peelability after several seconds of application, oily surface adhesion, a high-temperature finish without popping on the coated surface over a wide temperature distribution range of 70 to 120°C, and good blocking properties even after several minutes of application. However, because it contains a certain amount of alkyd resin, there is an issue with the drying speed of the coating film when applied in a factory at temperatures below 70°C.

[0004] Japanese Patent Application Laid-Open No. 2005-349684 (Patent Document 2) describes an invention that provides a resin-coated surface-treated steel sheet having a colorless and transparent resin film with excellent blocking resistance by using a core-shell emulsion resin in which the Tg of the outermost shell is higher than the Tg of the center of the particle.

[0005] Japanese Patent Publication No. 2020-2327 (Patent Document 3) describes an invention relating to an aqueous coating composition that can be used for both room-dry coating and baking coating, and that can form a coating film with excellent film-forming properties, blocking resistance, and rust prevention. This invention relates to an aqueous coating composition that contains a certain ratio of urethane resin particles with a glass transition temperature of 30 to 100°C and acrylic resin particles with a glass transition temperature of -20 to 30°C. The invention described in Patent Document 3 solves the issue of blocking resistance during factory painting by blending two types of resin components with different glass transition temperatures, but does not take into consideration film-forming properties and drying properties in the early stages of coating film formation, and there is also room for improvement in the water resistance of the resulting coating film. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 7-300574 [Patent Document 2] Japanese Patent Application Laid-Open No. 2005-349684 [Patent Document 3] Japanese Patent Publication No. 2020-2327 Summary of the Invention [Problem to be solved by the invention]

[0007] Therefore, an object of the present invention is to provide a coating composition that can form a coated body that has excellent coating film drying properties, excellent blocking resistance, and excellent water resistance when applied in a factory using an aqueous coating. [Means for solving the problem]

[0008] As a result of extensive research into achieving the above-mentioned object, the present inventors have found that by using an organic solvent as part of the solvent in an aqueous paint composition, adjusting the pigment volume concentration (PVC) within a specific range, and blending in a resin that has a spectral peak within a specific range in the temperature change curve of the loss tangent, it is possible to provide a paint composition that can form a coated body that has excellent coating film drying properties, excellent blocking resistance, and excellent water resistance when the aqueous paint is applied in a factory.

[0009] Therefore, a first aspect of the present invention is a coating composition containing water, an organic solvent, a pigment, and a resin, wherein the pigment volume concentration (PVC) is within the range of 0.1 to 35%, and the resin has at least one spectral peak in a temperature change curve of loss tangent (tanδ) measured at a measurement frequency of 1 Hz using a solid viscoelasticity measuring device based on JIS K7244-4, which is between 45°C and 180°C.

[0010] In a preferred embodiment of the coating composition of the present invention, the coating composition contains a crosslinking component.

[0011] In another preferred embodiment of the coating composition of the present invention, the crosslink density of a coating film formed from the coating composition is 1.0×10 -6 ~1.0×10 -2 (mol / cc).

[0012] In another preferred embodiment of the coating composition of the present invention, the coating film formed from the coating composition has two or more softening points, one of which is below 25°C and another of which is 45°C or higher.

[0013] In another preferred embodiment of the coating composition of the present invention, the resin contains 1 to 30 mass % of a resin having a molecular weight of less than 100,000 in the resin component, and 20 to 99 mass % of a resin having a molecular weight of 100,000 or more or a resin having a crosslinked structure in the resin component.

[0014] In another preferred embodiment of the coating composition of the present invention, the resin contains one or more monomers having an SP value in the range of 9.2 to 9.9 as constituent components, and the organic solvent contains one or more organic solvents having an SP value of 8.0 to 11.1 and a boiling point in the range of 160 to 260°C.

[0015] A second aspect of the present invention is a coating film obtained from the above coating composition, characterized in that the coating film is applied to a thickness of 100 μm on a preheated steel plate, and the surface drying time measured in accordance with JIS K 5600-3-2 (Barochini method) at a steel plate temperature of 35 to 45°C is 10 seconds to 5 minutes. [Effects of the Invention]

[0016] According to the first aspect of the present invention, it is possible to provide a coating composition that can form a coated body that has excellent coating film drying properties, excellent blocking resistance, and excellent water resistance when applying an aqueous coating in a factory.

[0017] According to the second aspect of the invention, it is possible to provide a coating film that has excellent drying properties when applied with a water-based paint in a factory, excellent blocking resistance, and excellent water resistance. DETAILED DESCRIPTION OF THE INVENTION

[0018] The present invention will be described in detail below.

[0019] One aspect of the present invention is a coating composition comprising water, an organic solvent, a pigment, and a resin.

[0020] The water used in the coating composition of the present invention is not particularly limited, but suitable examples include tap water, ion-exchanged water, distilled water, and other pure water. Furthermore, when storing the coating composition for a long period of time, water that has been sterilized by ultraviolet irradiation or the like may be used to prevent the growth of mold and bacteria. The amount of water in the coating composition of the present invention is preferably 20 to 60% by mass, and more preferably 30 to 50% by mass.

[0021] The coating composition of the present invention is preferably an aqueous coating composition. In this specification, the term "aqueous coating composition" refers to a coating composition containing water as the main solvent.

[0022] The coating composition of the present invention preferably contains an organic solvent, and more preferably a film-forming aid, from the viewpoint of ensuring the film-forming properties of the coating film and improving the drying properties of the coating film. Film-forming aids are generally organic solvents formulated for the purpose of imparting film-forming properties, and are not considered to be film-forming components. Examples of film-forming aids include propylene glycol, propylene glycol monomethyl ether (PGMME), propylene glycol monoethyl ether, propylene glycol monopropyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monoisopropyl ether, ethylene glycol mono-n-butyl ether, ethylene glycol mono-isobutyl ether, ethylene glycol mono-tert-butyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol monoisopropyl ether, diethylene glycol mono-n-butyl ether, diethylene glycol mono-isobutyl ether, diethylene glycol mono-tert-butyl ether, 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate, diethylene glycol diethyl ether, diethylene glycol dimethyl ether, and triethylene glycol monobutyl ether. The other organic solvent is not particularly limited, and any organic solvent commonly used in the paint industry can be used. For example, various organic solvents such as alcohol-based solvents, ketone-based solvents, ester-based solvents, ether-based solvents, and hydrocarbon-based solvents can be used, but it is preferable to include a water-soluble organic solvent.

[0023] Examples of alcohol-based solvents include methanol, ethanol, and butanol. Examples of ketone-based solvents include acetone, methyl ethyl ketone, and methyl isobutyl ketone. Examples of ester-based solvents include ethyl acetate and butyl acetate. Examples of ether-based solvents include ethylene glycol monoethyl ether and methyl carbitol. Solvents having both a hydroxyl group and an ether bond, such as ethylene glycol monoethyl ether and methyl carbitol, are classified as ether-based solvents, as described above. Examples of hydrocarbon-based solvents include aliphatic hydrocarbons, alicyclic hydrocarbons, and aromatic hydrocarbons. More specific examples include toluene, xylene, solvent naphtha, mineral spirits, hexane, cyclohexane, octane, and terpene oil.

[0024] In the coating composition of the present invention, the amount of organic solvent is preferably 0.1 to 20 mass %, more preferably 1 to 10 mass %. The organic solvent may be used alone or in combination of two or more.

[0025] The pigment used in the coating composition of the present invention is not particularly limited, and pigments commonly used in the coating industry such as anti-rust pigments, extender pigments, coloring pigments, etc. These pigments may be used alone or in combination of two or more.

[0026] The coating composition of the present invention preferably contains an anti-rust pigment from the viewpoint of use in line anti-corrosion coating. Examples of anti-rust pigments include zinc powder, zinc oxide, barium metaborate, calcium silicate, aluminum phosphate, condensed aluminum phosphate, aluminum tripolyphosphate, zinc phosphate, zinc phosphite, potassium phosphite, calcium phosphite, aluminum phosphite, calcium zinc phosphate, zinc aluminum phosphate, zinc phosphomolybdate, aluminum phosphomolybdate, magnesium phosphate, and vanadate / phosphate mixed pigments, with zinc phosphate being particularly preferred. The amount of the anti-rust pigment in the coating composition of the present invention is, for example, 1 to 8 mass%.

[0027] Examples of extender pigments include silica, talc, mica, calcium carbonate, barium sulfate, etc. In the coating composition of the present invention, the amount of the extender pigment is, for example, 1 to 40 mass %.

[0028] Examples of color pigments include titanium oxide, iron oxide, carbon black, yellow lead, molybdate orange, ultramarine, Prussian blue, phthalocyanine blue, phthalocyanine green, quinacridone red, naphthol red, benzimidazolone yellow, Hansa yellow, benzimidazolone orange, dioxazine violet, etc. In the coating composition of the present invention, the amount of color pigment is, for example, 1 to 10% by mass.

[0029] The coating composition of the present invention preferably has a pigment volume concentration (PVC) in the range of 0.1 to 35%, more preferably in the range of 1 to 30%, and even more preferably in the range of 5 to 25%. By setting the PVC within the above-specified range, water resistance and blocking resistance can be improved. If the PVC is too low, drying speed decreases, resulting in a decrease in initial water resistance. If the PVC is too high, water permeability increases, resulting in a decrease in corrosion resistance.

[0030] In this specification, pigment volume concentration (PVC) is the ratio of the total volume of pigment to the total volume of the film-forming components in a paint composition, and can be calculated from the composition and specific gravity of each component that makes up the film-forming components.

[0031] In this specification, the film-forming components refer to the components excluding volatile components such as water and organic solvents, and are the components that will ultimately form a coating film. In this specification, the components that remain when the coating composition is dried at 130°C for 60 minutes are considered to be the film-forming components. In the coating composition of the present invention, the amount of the film-forming components is, for example, 50 to 70% by mass, and preferably 55 to 65% by mass.

[0032] Resins used in the coating composition of the present invention include those commonly used in the coating industry, such as acrylic resins, silicone resins, acrylic silicone resins, styrene-acrylic copolymer resins, polyester resins, fluororesins, rosin resins, petroleum resins, coumarone resins, phenolic resins, urethane resins, melamine resins, urea resins, epoxy resins, cellulose resins, xylene resins, alkyd resins, aliphatic hydrocarbon resins, butyral resins, maleic acid resins, fumaric acid resins, vinyl resins, amine resins, and ketimine resins.

[0033] In the coating composition of the present invention, the content of the resin in the coating film-forming components is preferably 30 to 90 mass %. The resins may be used alone or in combination of two or more.

[0034] In the coating composition of the present invention, the resin has at least one spectral peak in a temperature change curve of loss tangent (tanδ) measured at a measurement frequency of 1 Hz using a solid viscoelasticity measuring device based on JIS K7244-4, which is preferably in the range of 45°C to 180°C, more preferably 50°C to 130°C, and even more preferably 60°C to 110°C.

[0035] When the spectral peak in the temperature curve of loss tangent for a resin is within the above-specified range, the use of such a resin can improve the blocking resistance of the resulting coating film. By setting the temperature of the spectral peak in the temperature curve of loss tangent higher than the maximum temperature at which the steel sheets are stacked (specifically, setting it to 45°C or higher), the resin maintains a crystalline state in the temperature range at which the steel sheets are stacked, allowing hard convex portions to be present randomly in the coating film, thereby improving blocking resistance. On the other hand, when only resins have a spectral peak below 45°C in the temperature curve of loss tangent, the resin softens in the temperature range at which the steel sheets are stacked, causing blocking.

[0036] The resin can be prepared, for example, by emulsifying a water-dispersible resin in water, or emulsion-polymerizing a monomer component, using a surfactant as needed, while applying forced shear force using a high-speed agitator or the like. Alternatively, a resin dispersion can be prepared by adding a surfactant as needed to a water-dispersible resin polymerized in an organic solvent medium and then subjecting the resin to phase inversion into water, and the organic solvent contained in the resin dispersion can be removed by distillation or the like as needed. Alternatively, a resin dispersion can be prepared by performing polymerization in water using water as the medium.

[0037] In order to prepare a resin having a spectral peak within the above-specified range in the temperature change curve of loss tangent, it is preferable to include in the resin a polymer component having a glass transition temperature (Tg) of 45 to 180°C, which is calculated by the FOX formula shown below. [FOX formula] 1 / Tg=W1 / Tg1+W2 / Tg2+···+Wi / Tgi+···+Wn / Tgn In the FOX formula, Tg written in the denominator on the left side represents the glass transition temperature (unit: K) of the polymer component consisting of N types of monomers, Tg(1, 2, i, N) represents the glass transition temperature (unit: K) of each monomer, W(1, 2, i, N) is the mass fraction of each monomer, and the relationship W1 + W2 +··· + Wi +··· + Wn = 1 holds. Here, the glass transition temperature of a monomer means the glass transition temperature of its homopolymer.

[0038] The details of the method for measuring the loss tangent (tan δ) of a resin are as follows: A resin is applied to a polypropylene (PP) plate preheated to 80°C using an applicator so that the dry film thickness is 40 to 100 μm, and the resin is forcedly dried at 80°C for 30 minutes to obtain an isolated resin film. The loss modulus and storage modulus of the isolated film are measured at each temperature under the following measurement conditions using a solid viscoelasticity measuring device (e.g., RSA-GII (manufactured by TA Instruments)). The loss tangent is calculated from the loss modulus and storage modulus, a temperature change curve of the loss tangent is created, and the spectral peak value of the loss tangent is read. <Measurement conditions> Temperature range: -50℃~200℃ Heating rate: 5℃ / min Measurement length: 24.0 mm Measurement width: 8.0 mm Frequency: 1Hz Distortion: 0.05%

[0039] The coating composition of the present invention preferably contains a crosslinking component. In this specification, a crosslinking component is a component that forms crosslinks in the resin that constitutes the coating film. By forming crosslinks in the coating film, blocking resistance in the initial stage of coating film formation can be improved, and the water resistance of the coating film after drying can be improved. When the resin is an emulsion resin, the type of crosslinking of the resin can be broadly divided into interparticle crosslinking and intraparticle crosslinking. Either interparticle crosslinking or intraparticle crosslinking is acceptable, but interparticle crosslinking is preferred. Furthermore, the coating composition containing a crosslinked resin can be in any of a one-component, two-component, or multi-component form.

[0040] To form intra-particle crosslinks, there are mentioned methods such as using a monomer having two or more polymerizable unsaturated double bonds in the molecule, such as divinylbenzene, ethylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, and allyl (meth)acrylate, as a crosslinking component; using a monomer having functional groups that react with each other at the temperature during emulsion polymerization reaction, such as a method using a monomer having a combination of functional groups, such as a carboxyl group and a glycidyl group, or a hydroxyl group and an isocyanate group, as a crosslinking component; and using a hydrolyzable silyl group-containing monomer that undergoes hydrolysis and condensation reaction, such as (meth)acryloxypropyltrimethoxysilane and (meth)acryloxypropylmethyldimethoxysilane, as a crosslinking component. Thus, when forming intra-particle crosslinks, the crosslinking component is often a structural unit of a resin.

[0041] To form interparticle crosslinks, a method can be used in which a combination of a monomer having a functional group such as a carboxyl group, a glycidyl group, a carbonyl group, a hydroxyl group, or the like and a crosslinking agent is used as a crosslinking component. When forming interparticle crosslinks, the crosslinking component is often a combination of a resin structural unit and a crosslinking agent.

[0042] Examples of carboxyl group-containing monomers that can be used for inter-particle crosslinking include (meth)acrylic acid, crotonic acid, itaconic acid, itaconic acid half ester, maleic acid, and maleic acid half ester. Examples of glycidyl group-containing monomers include glycidyl (meth)acrylate. Examples of carbonyl group-containing monomers include acrolein, diacetone (meth)acrylamide, formyl styrene, (meth)acryloxyalkyl propanal, diacetone (meth)acrylate, acetonyl (meth)acrylate, acetoacetoxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate-acetylacetate, butanediol-1,4-acrylate-acetylacrylate, vinyl ethyl ketone, and vinyl isobutyl ketone. Examples of hydroxyl group-containing monomers include 2-hydroxyethyl (meth)acrylate, 2(3)-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl acrylate. By using these monomers, functional groups such as carboxyl groups, glycidyl groups, carbonyl groups, and hydroxyl groups can be introduced into the resin.

[0043] Examples of crosslinking agents that can be used for interparticle crosslinking by reacting with carboxyl groups in the resin include epoxy group-containing silanes, oxazoline group-containing polymers, carbodiimides, ethylene glycol glycidyl ethers, and metal chelates such as titanium chelates. Examples of crosslinking agents that can be used for reacting with glycidyl groups in the resin include amino group-containing silanes. Examples of crosslinking agents that can be used for interparticle crosslinking by reacting with carbonyl groups in the resin include carbohydrazide, oxalic acid dihydrazide, and malonic acid dihydrazide. Examples of crosslinking agents that can be used for interparticle crosslinking by reaction with hydroxyl groups in the resin include metal alkoxides such as titanium alkoxide and zirconium alkoxide, and metal chelates such as titanium chelate.

[0044] In a preferred embodiment of the coating composition of the present invention, the crosslink density of the coating film formed from the coating composition is 1.0 × 10 -6 ~1.0×10 -2 (mol / cc) range. The crosslink density of the coating film is an index showing the degree of crosslinking structure formed in the coating film; the higher this value, the higher the proportion of crosslinking structure formed in the coating film. By keeping the crosslink density of the coating film within the above specified range, blocking resistance in the early stages of coating film formation can be improved, and the water resistance of the coating film after drying can be improved.

[0045] In this specification, the crosslink density of the coating film is calculated by the formula n=E' / 3RT (where n is the crosslink density (mol / cc) of the coating film, E' is the plateau storage modulus (Pa) of the coating film at a frequency of 1 Hz, T is the absolute temperature (K) of the plateau storage modulus of the coating film, and R is the gas constant (8.31 x 10 6 ) is calculated from the following:

[0046] The details of the method for measuring the plateau storage modulus of a coating film are as follows: A coating composition is applied to a polypropylene (PP) plate, which has been preheated to 80°C, using an applicator so that the dry film thickness is 40 to 100 μm, and the plate is forced dried at 80°C for 30 minutes to obtain an isolated film. The storage modulus of the isolated film is measured using a solid viscoelasticity measuring device (for example, RSA-GII (manufactured by TA Instruments)) under the following measurement conditions, and the plateau storage modulus of the coating film is read. <Measurement conditions> Temperature range: -50℃~200℃ Heating rate: 5℃ / min Measurement length: 24.0 mm Measurement width: 8.0 mm Frequency: 1Hz Distortion: 0.05%

[0047] In a preferred embodiment of the coating composition of the present invention, the coating film formed from the coating composition has two or more softening points, one of which is below 25°C, preferably 5°C or higher but lower than 25°C, and another of which is 45°C or higher, preferably 50 to 100°C. When the coating film has a softening point below 25°C (particularly by including components whose temperature is lower than the coating film formation temperature), coating film formation is facilitated and a dense film is formed, improving the water resistance of the coating film. Furthermore, when the coating film has a softening point of 45°C or higher (particularly by including components whose temperature is higher than the maximum temperature experienced when steel sheets are stacked), blocking resistance is improved.

[0048] To obtain a coating film having at least a softening point of less than 25°C and a softening point of 45°C or higher, for example, a method of using a resin having a softening point of less than 25°C and a resin having a softening point of 45°C or higher in a coating composition, or a method of using resin particles having a heterogeneous phase structure having a phase having a softening point of less than 25°C and a phase having a softening point of 45°C or higher in a coating composition, can be mentioned.

[0049] In this specification, the softening point of a coating film refers to Tg1 (the temperature at which molecules begin to move) in viscoelasticity measurements. Details of the method for measuring the softening point of a coating film are as follows: A coating composition is applied to a polypropylene (PP) plate, which has been preheated to 80°C, using an applicator so that the dry film thickness is 40 to 100 μm, and the film is forced dried at 80°C for 30 minutes to obtain an isolated film. The storage modulus of the isolated film is measured under the following measurement conditions using a solid viscoelasticity measuring device (for example, RSA-GII (manufactured by TA Instruments)), and the change point of the storage modulus (the temperature at which the drop begins) is designated as Tg1, which is the softening point. <Measurement conditions> Temperature range: -50℃~200℃ Heating rate: 5℃ / min Measurement length: 24.0 mm Measurement width: 8.0 mm Frequency: 1Hz Distortion: 0.05%

[0050] In a preferred embodiment of the coating composition of the present invention, the resin comprises a resin with a molecular weight of less than 100,000, preferably between 10,000 and 100,000, and a resin with a molecular weight of 100,000 or more or a resin with a crosslinked structure. The inclusion of a resin with a molecular weight of 100,000 or more or a resin with a crosslinked structure (preferably an emulsion resin) in the resin component improves the water resistance of the coating film. Generally, emulsion resins obtained by emulsion polymerization tend to have large molecular weights, and emulsion resins with crosslinked structures in particular cannot be accurately measured by gel permeation chromatography, so they are not measurable in this specification. Furthermore, the inclusion of a resin with a molecular weight of less than 100,000 in the resin component, which fills the gaps in the emulsion resin during film formation, improves the overall density of the coating film, resulting in a coating film with better water resistance. The resin with a molecular weight of less than 100,000 is preferably a dispersion resin or a water-soluble resin.

[0051] In this specification, emulsion resin refers to a water-dispersible resin obtained by emulsion polymerization. Dispersion resin refers to a self-water-dispersible resin, but in this specification, emulsion resins are excluded. Water-soluble resin is a resin that dissolves in water.

[0052] In the coating composition of the present invention, the resin having a molecular weight of less than 100,000 is preferably contained in the resin component in an amount of 1 to 30% by mass, more preferably 3 to 25% by mass. Furthermore, the resin having a molecular weight of 100,000 or more or the resin having a crosslinked structure is preferably contained in the resin component in an amount of 20 to 99% by mass, more preferably 70 to 99% by mass. In this specification, the term "resin component" refers to the entire resin in the coating composition.

[0053] The weight-average molecular weight of the resin having a crosslinked structure is preferably 100,000 or more, more preferably 300,000 or more, even more preferably 550,000 or more, and particularly preferably 600,000 or more, from the viewpoint of obtaining an aqueous resin composition and an aqueous coating material that are excellent overall in hot water whitening resistance, freeze-thaw resistance, and blocking resistance. The upper limit of the weight-average molecular weight of the resin having a crosslinked structure is not particularly limited because it is difficult to measure the weight-average molecular weight accurately due to the crosslinked structure of the resin, but from the viewpoint of improving hot water whitening resistance and freeze-thaw resistance, it is preferably 5,000,000 or less.

[0054] In this specification, the molecular weight of a resin is the weight-average molecular weight measured by gel permeation chromatography (e.g., Tosoh Corporation's HLC-8220GPC and HLC-8320EcoSEC instruments), with polystyrene used as the standard. The measurement sample is prepared by dissolving 20-40 mg of resin in 10 ml of tetrahydrofuran or dimethylformamide reagent, then filtering through a filter (e.g., PTFE membrane filter T100A025A) and measuring. If the sample solution is opaque or the filter is clogged at this point, accurate molecular weight measurement is not possible and the measurement is deemed unsuccessful.

[0055] In an embodiment of the coating composition of the present invention, the resin contains resin particles having a heterophase structure, and is preferably a core-shell emulsion, a sea-island emulsion, or a multilayer emulsion having at least two glass transition temperatures: one below 45°C, preferably 0 to 40°C, and the other between 55°C and 95°C, preferably 60 to 90°C. If a portion of the resin particles has a glass transition temperature in the low temperature range, preferably below 45°C, film-forming properties and, in turn, corrosion prevention properties can be improved. Furthermore, if a portion of the resin particles has a glass transition temperature in the high temperature range, preferably between 55°C and 95°C, blocking resistance can be improved.

[0056] In this specification, the details of the method for measuring the glass transition temperature of a resin are as follows: A resin is applied to a polypropylene (PP) plate preheated to 80°C using an applicator so that the dry film thickness is 40 to 100 μm, and the resin is forcedly dried at 80°C for 30 minutes to obtain an isolated film of the resin. The loss modulus of the isolated film is measured under the following measurement conditions using a solid viscoelasticity measuring device (for example, RSA-GII (manufactured by TA Instruments)), and the maximum value of the loss modulus is read as the glass transition temperature. <Measurement conditions> Temperature range: -50℃~200℃ Heating rate: 5℃ / min Measurement length: 24.0 mm Measurement width: 8.0 mm Frequency: 1Hz Distortion: 0.05%

[0057] Resin particles having a heterogeneous phase structure can be obtained, for example, by a multistage emulsion polymerization method.

[0058] A multistage emulsion polymerization method that can be used to produce resin particles having a heterophase structure includes a multistage emulsion polymerization method in which an aqueous emulsion containing an ethylenically unsaturated monomer is formed, and a conventionally known emulsion polymerization method is repeatedly carried out in two or more stages, usually two to five stages, to form an emulsion copolymer of the ethylenically unsaturated monomer having a heterophase structure, i.e., particles consisting of an outermost phase and one or more internal phases having different properties.

[0059] A typical example of the multistage emulsion polymerization method is a multistage emulsion polymerization method in which an emulsifier and a polymerization initiator, and optionally a chain transfer agent, an emulsion stabilizer, and the like are present in an aqueous emulsion containing an ethylenically unsaturated monomer, and emulsion polymerization is carried out usually at a temperature of 60 to 90°C, and this process is repeated multiple times.

[0060] Furthermore, examples of ethylenically unsaturated monomers that can be used to form resin particles having a heterophase structure include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, pentyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, decyl (meth)acrylate, dodecyl (meth)acrylate, stearyl (meth)acrylate, and α-chloroethyl (meth)acrylate. (Meth)acrylate monomers such as cyclohexyl (meth)acrylate, phenyl (meth)acrylate, methoxyethyl (meth)acrylate, ethoxyethyl (meth)acrylate, methoxypropyl (meth)acrylate, and ethoxypropyl (meth)acrylate; styrene and / or methylstyrene, chlorostyrene, methoxystyrene, and other styrene derivatives; carboxyl group-containing monomers such as (meth)acrylic acid, crotonic acid, itaconic acid, itaconic acid half ester, maleic acid, and maleic acid half ester. monomers; hydroxyl group-containing monomers such as 2-hydroxyethyl (meth)acrylate, 2(3)-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl acrylate; amide group-containing monomers such as (meth)acrylamide and maleinamide; amino group-containing monomers such as 2-aminoethyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, 3-aminopropyl (meth)acrylate, 2-butylaminoethyl (meth)acrylate, and vinylpyridine; glycidyl (meth)acrylate and allyl glycidyl Epoxy group-containing monomers and oligomers obtained by reacting glycidyl ethers, epoxy compounds having two or more glycidyl groups with ethylenically unsaturated monomers having active hydrogen atoms; N-methylolacrylamide having an N-methylol group; UV-stable monomers such as 4-(meth)-acryloyloxy-2,2,6,6-tetramethylpiperidine, 4-(meth)-acryloylamino-2,2,6,6-tetramethylpiperidine, and 4-(meth)-acryloyloxy-1,2,2,6,6-pentamethylpiperidine;Representative examples include ultraviolet absorbing monomers such as 2-[2'-hydroxy-5'-(methacryloyloxymethyl)phenyl]-2H-benzotriazole and 2-[2'-hydroxy-5'-(methacryloyloxyethyl)phenyl]-2H-benzotriazole; vinyl acetate, vinyl chloride, ethylene, butadiene, acrylonitrile, and dialkyl fumarate;

[0061] Preferably, the polymer forming at least one phase of the resin particles having heterophase structure has internal crosslinking structure.The polymer having internal crosslinking structure can be produced by the emulsion polymerization method using the monomer having two or more polymerizable unsaturated double bonds in the molecule as part of ethylenically unsaturated monomer, such as divinylbenzene, ethylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, allyl (meth)acrylate, etc.; the emulsion polymerization method using the monomer mixture containing the ethylenically unsaturated monomer having the functional group combination of the monomers that react with each other at the temperature of emulsion polymerization reaction, for example, the functional group combination of carboxyl group and glycidyl group, hydroxyl group and isocyanate group, etc.; the emulsion polymerization method using the monomer mixture containing the silyl group-containing ethylenically unsaturated monomer that undergoes hydrolysis condensation reaction, such as (meth)acryloxypropyltrimethoxysilane, (meth)acryloxypropyltriethoxysilane, (meth)acryloxypropylmethyldimethoxysilane, etc.

[0062] Examples of emulsifiers that can be used to form resin particles having a heterogeneous phase structure include anionic surfactants such as fatty acid salts such as sodium laurate, higher alcohol sulfate salts such as sodium lauryl sulfate, alkylbenzene sulfonates such as sodium dodecylbenzenesulfonate, polyoxyethylene alkyl ether sulfates, ammonium polyoxynonylphenyl ether sulfonate, polyoxyethylene-polyoxypropylene glycol ether sulfates, and so-called reactive emulsifiers having a sulfonic acid group or a sulfate ester group and a polymerizable carbon-carbon unsaturated double bond in the molecule; nonionic surfactants such as polyoxyethylene alkyl ethers, polyoxyethylene nonylphenyl ethers, sorbitan fatty acid esters, polyoxyethylene fatty acid esters, polyoxyethylene-polyoxypropylene block copolymers, or reactive nonionic surfactants having a skeleton of these compounds and a polymerizable carbon-carbon unsaturated double bond in the molecule; cationic surfactants such as alkylamine salts and quaternary ammonium salts; and (modified) polyvinyl alcohol.

[0063] Examples of emulsifiers include anionic emulsifiers, nonionic emulsifiers, cationic emulsifiers, amphoteric emulsifiers, and polymeric emulsifiers. These emulsifiers may be used alone or in combination of two or more.

[0064] Examples of anionic emulsifiers include alkyl sulfate salts such as ammonium dodecyl sulfate and sodium dodecyl sulfate; alkyl sulfonate salts such as ammonium dodecyl sulfonate, sodium dodecyl sulfonate and sodium alkyl diphenyl ether disulfonate; alkyl aryl sulfonate salts such as ammonium dodecyl benzene sulfonate and sodium dodecyl naphthalene sulfonate; polyoxyethylene alkyl sulfonate salts; polyoxyethylene alkyl sulfate salts; polyoxyethylene alkyl aryl sulfate salts; dialkyl sulfosuccinate salts; aryl sulfonic acid-formalin condensates; and an fatty acid salts such as ammonium laurate and sodium stearylate; sulfates or salts thereof having an allyl group such as bis(polyoxyethylene polycyclic phenyl ether) methacrylate sulfonate salts, propenyl-alkyl sulfosuccinate ester salts, (meth)acrylic acid polyoxyethylene sulfonate salts, (meth)acrylic acid polyoxyethylene phosphonate salts, and sulfonate salts of allyloxymethyl alkyloxy polyoxyethylene; sulfate salts of allyloxymethyl alkoxyethyl polyoxyethylene, and polyoxyalkylene alkenyl ether ammonium sulfate salts, but the present invention is not limited to these examples.

[0065] Examples of nonionic emulsifiers include polyoxyethylene alkyl ethers, polyoxyethylene alkylaryl ethers, condensates of polyethylene glycol and polypropylene glycol, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, fatty acid monoglycerides, condensation products of ethylene oxide and aliphatic amines, allyloxymethylalkoxyethylhydroxypolyoxyethylene, and polyoxyalkylene alkenyl ethers, but the present invention is not limited to these examples.

[0066] Examples of cationic emulsifiers include alkylammonium salts such as dodecylammonium chloride, but the present invention is not limited to these examples.

[0067] Examples of amphoteric emulsifiers include betaine ester emulsifiers, but the present invention is not limited to these examples.

[0068] Examples of polymeric emulsifiers include poly(meth)acrylates such as sodium polyacrylate; polyvinyl alcohol; polyvinylpyrrolidone; polyhydroxyalkyl(meth)acrylates such as polyhydroxyethyl acrylate; and copolymers containing one or more of the monomers constituting these polymers as copolymerization components, but the present invention is not limited to these examples.

[0069] Furthermore, from the viewpoint of obtaining an aqueous resin composition and an aqueous coating composition that are excellent overall in hot water whitening resistance, freeze-thaw resistance, and blocking resistance, an emulsifier having a polymerizable group, i.e., a so-called reactive emulsifier, is preferred as the emulsifier, and from the viewpoint of environmental protection, a non-nonylphenyl type emulsifier is preferred.

[0070] Examples of the reactive emulsifier include propenyl-alkyl sulfosuccinate salts, (meth)acrylic acid polyoxyethylene sulfonate salts, (meth)acrylic acid polyoxyethylene phosphonate salts (e.g., Sanyo Chemical Industries, Ltd., trade name: Eleminol RS30, etc.), polyoxyethylene alkylpropenylphenyl ether sulfonate salts (e.g., Dai-ichi Kogyo Seiyaku Co., Ltd., trade name: Aqualon HS-10, etc.), sulfonate salts of allyloxymethyl alkyloxypolyoxyethylene (e.g., Dai-ichi Kogyo Seiyaku Co., Ltd., trade name: Aqualon KH-10, etc.), sulfonate salts of allyloxymethyl nonylphenoxyethyl hydroxypolyoxyethylene (e.g., ADEKA Corporation, trade name: Adeka Reasoap SE-10, etc.), allyloxymethyl alkoxyethyl hydroxypolyoxyethylene (e.g., ADEKA Corporation, trade name: Adeka Reasoap SE-10, etc.), and the like. Examples of suitable polyoxyethylene sulfate salts include polyoxyethylene sulfate salts (e.g., manufactured by ADEKA CORPORATION under the trade names ADEKA REASOAP SR-10 and SR-30), bis(polyoxyethylene polycyclic phenyl ether) methacrylated sulfonate salts (e.g., manufactured by Nippon Nyukazai Co., Ltd. under the trade name ANTOX MS-60), allyloxymethylalkoxyethylhydroxypolyoxyethylene (e.g., manufactured by ADEKA CORPORATION under the trade name ADEKA REASOAP ER-20), polyoxyethylene alkylpropenylphenyl ether (e.g., manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd. under the trade name AQUALON RN-20), and allyloxymethylnonylphenoxyethylhydroxypolyoxyethylene (e.g., manufactured by ADEKA CORPORATION under the trade name ADEKA REASOAP NE-10). However, the present invention is not limited to these examples.

[0071] In forming resin particles having a heterophase structure, polymerization initiators commonly used in radical polymerization can be used, with water-soluble initiators being preferred. Examples include persulfates such as potassium persulfate and ammonium persulfate; azo compounds such as 2,2'-azobis(2-aminodipropane) hydrochloride, 4,4'-azobis-cyanovaleric acid, and 2,2'-azobis(2-methylbutanamidoxime) dihydrochloride tetrahydrate; and peroxides such as hydrogen peroxide and t-butyl hydroperoxide. Redox systems combining reducing agents such as L-ascorbic acid and sodium thiosulfate with ferrous sulfate can also be used.

[0072] Examples of chain transfer agents that can be used to form resin particles having a heterogeneous phase structure include alkyl mercaptans, aromatic mercaptans, and halogenated hydrocarbons, and among these, preferred are lauryl mercaptan, n-butyl mercaptan, t-butyl mercaptan, octyl mercaptan, n-dodecyl mercaptan, 2-ethylhexyl thioglycolate, 2-methyl-t-butylthiophenol, carbon tetrabromide, and α-methylstyrene dimer. By using these agents appropriately, the gloss, film-forming properties, and non-stickiness of the coating film can be controlled.

[0073] Examples of emulsion stabilizers that can be used to form resin particles having a heterogeneous phase structure include polyvinyl alcohol, hydroxyethyl cellulose, and polyvinylpyrrolidone.

[0074] Examples of emulsion polymerization methods include a batch monomer charging method in which the monomers are charged all at once, a monomer dropping method in which the monomers are continuously dropped, a pre-emulsion method in which the monomers, water, and an emulsifier are mixed and emulsified in advance and the resulting mixture is dropped, and a combination of these methods.

[0075] In the present invention, when producing resin particles having a heterogeneous phase structure by the above-mentioned method, it is preferable to appropriately select a combination of ethylenically unsaturated monomers so that the theoretical Tg, calculated from the FOX formula, of the polymer forming part of the resin particles is 55°C to 95°C, preferably 60 to 90°C, and it is also preferable to appropriately select a combination of ethylenically unsaturated monomers so that the theoretical Tg, calculated from the FOX formula, of the polymer forming part of the resin particles is less than 45°C, preferably 0 to 40°C.

[0076] In a preferred embodiment of the coating composition of the present invention, the resin contains one or more monomers with an SP value in the range of 9.2 to 9.9 as constituent components, and the organic solvent contains one or more organic solvents with an SP value of 8.0 to 11.1 (more preferably 8.5 to 11.1) and a boiling point in the range of 160 to 260°C. By using a monomer with an SP value similar to that of the organic solvent as a constituent component of the resin, the film-forming effect of the organic solvent can be more reliably demonstrated, softening the resin during film formation and facilitating film formation. Furthermore, the boiling point of the organic solvent in the range of 160 to 260°C prevents the surface of the coating from drying out, and the organic solvent is less likely to remain in the coating. Therefore, this embodiment can be a coating composition that is superior for factory application.

[0077] The SP value (solubility parameter) is a guideline for determining compatibility, and there are various calculation and measurement methods. In this specification, the SP value refers to the solubility parameter calculated by the Hoy method based on the structure. Here, the SP value of a monomer refers to the SP value of a homopolymer of the monomer, and is a value calculated using the vapor pressure method proposed by Hoy in accordance with the method described in the literature [KL Hoy, J. Paint Technology, 42,

[0541] , 76 (1970)]. Specifically, the SP value is expressed as δ = (dΣG) / M, where d is the density of the polymer, M is the molecular weight of the basic structural unit of the polymer, and ΣG is the sum of the molecular attraction constants G corresponding to the atoms (groups) present in the basic structural unit. The SP value of an organic solvent is a value calculated using the vapor pressure method proposed by Hoy in accordance with the method described in the literature [KL Hoy, J. Paint Technology, 42,

[0541] , 76 (1970)].

[0078] Examples of monomers having an SP value in the range of 9.2 to 9.9 include methyl methacrylate (9.5), ethyl methacrylate (9.4), n-butyl acrylate (9.7), isopropyl acrylate (9.8), isobutyl acrylate (9.4), isobutyl methacrylate (9.3), 2-ethylhexyl acrylate (9.2), pentyl acrylate (9.6), cyclohexyl methacrylate (9.5), and styrene (9.4). The values ​​in parentheses indicate the SP values ​​of the monomers. The proportion of monomers having an SP value of 9.2 to 9.9 in the resin constituents is preferably 85 to 98% by mass.

[0079] Examples of organic solvents having an SP value in the range of 8.0 to 11.1 and a boiling point in the range of 160 to 260°C include ethylene glycol mono-n-butyl ether (SP value: 11.0, boiling point: 170°C), diethylene glycol monopropyl ether (SP value: 11.1, boiling point: 214°C), diethylene glycol monoisopropyl ether (SP value: 10.9, boiling point: 207°C), diethylene glycol mono-n-butyl ether (SP value: 10.9, boiling point: 230°C), diethylene glycol monoisobutyl ether (SP value: 10.7, boiling point: 220°C), 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate (SP value: 9.9, boiling point: 255°C), diethylene glycol diethyl ether (SP value: 9.5, boiling point: 189°C), and diethylene glycol dimethyl ether (SP value: 9.7, boiling point: 162°C). The proportion of the organic solvent having an SP value of 8.0 to 11.1 and a boiling point of 160 to 260° C. relative to the total amount of organic solvents is preferably 50 to 100 mass %. In this specification, boiling point refers to the boiling point at 1 atmospheric pressure.

[0080] Other components that can be appropriately blended into the coating composition of the present invention include surface conditioners, wetting agents, dispersants, emulsifiers, thickeners, anti-settling agents, anti-skinning agents, anti-dripping agents, anti-foaming agents, anti-color separation agents, viscosity adjusters, rheology control agents, leveling agents, antifoaming agents, drying agents, plasticizers, preservatives, anti-mold agents, antibacterial agents, insecticides, light stabilizers, ultraviolet absorbers, antistatic agents, and conductivity imparting agents, depending on the purpose.

[0081] The coating composition of the present invention can be prepared by mixing various components appropriately selected as needed. The coating composition of the present invention may be either a one-component type in which the various components are premixed and used as is at the time of application, or a multi-component type (e.g., two-component type) in which two or more components (e.g., base resin and curing agent) that have been stored separately are mixed at the time of application.

[0082] The minimum film-forming temperature (MFT) of the coating composition of the present invention is preferably 5 to 25° C., and more preferably 10 to 20° C. For example, when a resin with a high glass transition temperature is used, the minimum film-forming temperature becomes high, but it is possible to set the minimum film-forming temperature low by appropriately blending an organic solvent, preferably a film-forming aid.

[0083] In this specification, the minimum film-forming temperature is the minimum temperature at which a crack-free, uniform coating film is formed when the coating composition is dried, and is measured in accordance with JIS K 6828-2:2003.

[0084] The coating composition of the present invention preferably has a viscosity of 1 to 1000 (Pa s, 23°C) at a shear rate of 0.1 (1 / s), and a viscosity of 0.05 to 10 (Pa s, 23°C) at a shear rate of 1000 (1 / s). In this specification, viscosity is measured using a rheometer (for example, ARES rheometer manufactured by TA Instruments) after adjusting the liquid temperature to 23°C.

[0085] The means for applying the coating composition of the present invention is not particularly limited, and known coating means such as brush coating, roller coating, trowel coating, spatula coating, flow coater coating, and spray coating (e.g., air spray coating, airless spray coating, etc.) can be used.

[0086] The means for drying the coating composition of the present invention is not particularly limited, and may be either natural drying at ambient temperature or forced drying using a dryer or the like.

[0087] The coating composition of the present invention can be applied under various coating conditions, such as general factory line coating conditions (forced drying, film thickness 15 to 30 μm) and conditions conforming to JIS K5674 standards (ambient drying, film thickness 30 μm).

[0088] Another aspect of the present invention is a coating film obtained from the coating composition of the present invention. The contents described in the description of the coating composition of the present invention also apply to the coating film of the present invention.

[0089] In a preferred embodiment of the coating film of the present invention, a 100 μm coating is applied to a preheated steel plate, and the steel plate is maintained at 35 to 45°C. The surface drying time measured in accordance with JIS K 5600-3-2 (by the Ballochny method) is 10 seconds or more and less than 10 minutes, preferably 10 seconds to 5 minutes. Here, "preheated steel plate" refers to a steel plate whose surface temperature is maintained at 35 to 45°C. The "100 μm" value for "100 μm coating" refers to the film thickness immediately after coating and before drying. A surface drying time of 10 seconds to 5 minutes under these conditions results in a coating film with excellent drying properties when applied in the factory, enabling the formation of a coated body with excellent blocking resistance.

[0090] The coating film of the present invention preferably has a thickness of 10 to 200 μm, more preferably 20 to 170 μm, and even more preferably 50 to 150 μm. A thin coating film tends to have poor corrosion resistance, while a thick coating film tends to have poor drying properties (and hence poor drying properties, which leads to poor initial water resistance) and poor blocking resistance. Therefore, a coating film having a thickness within the above-specified range is preferred. Furthermore, when the coating film has a thickness as thin as 10 to 50 μm, corrosion resistance is improved by including an epoxy resin as the resin having a molecular weight of less than 100,000, and a vinyl-modified epoxy resin is particularly preferred.

[0091] The vinyl-modified epoxy resin is not particularly limited, but examples include reaction products composed of components such as a bisphenol-type epoxy resin, a glycidyl group-containing polymerizable vinyl monomer, and amines, and optionally reactive components. That is, the epoxy groups in the bisphenol-type epoxy resin are ring-opened by the amines, and simultaneously, amino groups are introduced into the epoxy resin, which is thought to further improve the inherent performance of unmodified epoxy resins, such as adhesion. Furthermore, the glycidyl group-containing polymerizable vinyl monomer reacts with the epoxy groups in the bisphenol-type epoxy resin via the amines, thereby introducing polymerizable unsaturated groups into the epoxy resin, imparting copolymerizability.

[0092] Other examples of the vinyl-modified epoxy resin include a resin obtained by graft polymerizing a polymerizable unsaturated monomer component containing a carboxyl group-containing polymerizable unsaturated monomer onto a bisphenol-type epoxy resin. The resin can be graft polymerized with the polymerizable unsaturated monomer component onto the epoxy resin, for example, in an organic solvent in the presence of a radical generator such as benzoyl peroxide.

[0093] In a preferred embodiment of the coating film of the present invention, the crosslink density of the coating film is 1.0×10 -6 ~1.0×10 -2 (mol / cc) range. The crosslink density of the coating film is an index showing the degree of crosslinking structure formed in the coating film; the higher this value, the higher the proportion of crosslinking structure formed in the coating film. By keeping the crosslink density of the coating film within the above specified range, blocking resistance in the early stages of coating film formation can be improved, and the water resistance of the coating film after drying can be improved.

[0094] In a preferred embodiment of the coating film of the present invention, the coating film has two or more softening points, one of which is below 25°C, preferably between 5 and 25°C, and another of which is 45°C or higher, preferably between 50 and 100°C. When the coating film has a softening point below 25°C (particularly by including components that are lower than the coating film formation temperature), coating film formation is facilitated and a dense film is formed, improving the water resistance of the coating film. On the other hand, when the coating film has a softening point of 45°C or higher (particularly by including components that are higher than the maximum temperature to which the steel sheets are exposed when stacked), blocking resistance is improved.

[0095] In a preferred embodiment of the coating film of the present invention, the coating film contains resin particles having a heterogeneous phase structure, and the heterogeneous phase structure is preferably a core-shell emulsion, a sea-island emulsion, or a multilayer emulsion having at least two glass transition temperatures: one below 45°C, preferably 0 to 40°C, and the other between 55°C and 95°C, preferably 60 to 90°C, and the resin particles are crosslinked between themselves. If a portion of the resin particles has a glass transition temperature in the low temperature range, preferably below 45°C, film-forming properties and, in turn, corrosion prevention properties can be improved. Furthermore, if a portion of the resin particles has a glass transition temperature in the high temperature range, preferably between 55°C and 95°C, blocking resistance can be improved.

[0096] In the coating film forming method of the present invention, the substrate to be coated is not particularly limited, but suitable examples include metal substrates containing at least a metal or alloy such as steel, zinc-plated steel (e.g., galvanized sheet), tin-plated steel (e.g., tin plate), stainless steel, magnesium alloy, aluminum, aluminum alloy, etc. The coating composition of the present invention is particularly suitable for coating steel materials such as steel bars, steel plates, and steel pipes.

[0097] Specific examples of substrates include various building materials, as well as structures such as buildings and structures and their components. In this specification, a building refers to a structure built for the purpose of human habitation or stay, such as a house, a building, or a factory, while a structure refers to a structure built for purposes other than human habitation or stay, such as a bridge, a tank, plant piping, or a chimney. Examples of components of buildings and structures include roofs and walls.

[0098] The substrate may also have been subjected to various surface treatments, such as oxidation treatment or primer treatment, and may have an old coating film (a coating film already formed when painting) on ​​at least a portion of its surface. [Example]

[0099] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples. In the resin synthesis examples, "parts" and "%" are by mass unless otherwise specified.

[0100] <Synthesis of acrylic emulsion> <Acrylic Emulsion A> A flask equipped with a stirrer, a reflux condenser, a thermometer, a dropping device, and a nitrogen inlet tube was charged with 40.0 parts of ion-exchanged water, 0.5 parts of α-sulfonato-ω-(1-(allyloxymethyl)-alkyloxypolyoxyethylene)ammonium salt (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.; AQUALON KH10), and 0.2 parts of 2-polyoxyethylene-4-nonyl-2-propenylphenyl ether (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.; AQUALON RN20). The atmosphere in the flask was replaced with nitrogen, and the temperature was raised to 80°C. Then, 0.2 parts of ammonium persulfate was added. Next, a pre-emulsion for dropping was prepared, consisting of a monomer emulsion of 15.5 parts of methyl methacrylate, 1.5 parts of butyl acrylate, 1.8 parts of styrene, 1.2 parts of an 80% aqueous solution of acrylic acid, 11.0 parts of ion-exchanged water, 1.0 part of α-sulfonato-ω-(1-(allyloxymethyl)-alkyloxypolyoxyethylene)ammonium salt (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.; Aqualon KH10), and 0.5 parts of 2-polyoxyethylene-4-nonyl-2-propenylphenyl ether (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.; Aqualon RN20), and this pre-emulsion was added dropwise uniformly into the flask over 120 minutes. After the dropwise addition was completed, the contents of the flask were maintained at 80°C for 60 minutes. Subsequently, while maintaining the temperature in the flask at 80°C, a monomer emulsion containing 2.0 parts of styrene, 9.6 parts of butyl acrylate, 9.4 parts of methyl methacrylate, 2.0 parts of 2-hydroxyethyl methacrylate, 1.0 parts of glycidyl methacrylate, 10.0 parts of ion-exchanged water, 0.2 parts of α-sulfonato-ω-(1-(allyloxymethyl)-alkyloxypolyoxyethylene)ammonium salt (Dai-ichi Kogyo Seiyaku Co., Ltd.; Aqualon KH10), and 0.1 parts of 2-polyoxyethylene-4-nonyl-2-propenylphenyl ether (Dai-ichi Kogyo Seiyaku Co., Ltd.; Aqualon RN20) was prepared and added dropwise to the flask uniformly over 120 minutes. After the dropwise addition was completed, the mixture was further aged for 120 minutes with continued stirring. The mixture was cooled to room temperature and adjusted to a solids content of 43% and a pH of 8.5 to obtain Acrylic Emulsion A. The glass transition temperatures of the first-stage emulsion particles contained in the resin emulsion obtained above were 84.9°C, the second-stage emulsion particles were 15.0°C, and the entire emulsion particles had a glass transition temperature of 42.8°C.Furthermore, since Acrylic Emulsion A contains a crosslinked structure, the molecular weight could not be measured.

[0101] <Acrylic Emulsion B> A flask equipped with a stirrer, a reflux condenser, a thermometer, a dropping device, and a nitrogen inlet tube was charged with 31.0 parts of ion-exchanged water, 0.5 parts of α-sulfonato-ω-(1-(allyloxymethyl)-alkyloxypolyoxyethylene)ammonium salt (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.; AQUALON KH10), and 0.2 parts of 2-polyoxyethylene-4-nonyl-2-propenylphenyl ether (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.; AQUALON RN20). The atmosphere in the flask was replaced with nitrogen, and the temperature was raised to 80°C. Then, 0.2 parts of ammonium persulfate was added. A pre-emulsion for dropping was prepared from the monomers: 18.0 parts methyl methacrylate, 17.0 parts butyl acrylate, 13.0 parts styrene, 1.2 parts 80% aqueous acrylic acid solution, 21.0 parts ion-exchanged water, 1.5 parts α-sulfonato-ω-(1-(allyloxymethyl)-alkyloxypolyoxyethylene)ammonium salt (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.; Aqualon KH10), and 1.0 part 2-polyoxyethylene-4-nonyl-2-propenylphenyl ether (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.; Aqualon RN20). This pre-emulsion was added dropwise to the flask over 120 minutes. After the dropwise addition, the mixture was further aged for 120 minutes with continued stirring. The mixture was cooled to room temperature and adjusted to a solids content of 50% and a pH of 8.0 to obtain Acrylic Emulsion B. The glass transition temperature of the resulting Acrylic Emulsion B was 28.1°C. Furthermore, the weight-average molecular weight of Acrylic Emulsion B measured using GPC was greater than 100,000.

[0102] <Acrylic Emulsion C> A flask equipped with a stirrer, reflux condenser, thermometer, dropping device, and nitrogen inlet tube was charged with 31.0 parts of ion-exchanged water, 0.5 parts of α-sulfonato-ω-(1-(allyloxymethyl)-alkyloxypolyoxyethylene)ammonium salt (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.; Aqualon KH10), and 0.2 parts of 2-polyoxyethylene-4-nonyl-2-propenylphenyl ether (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.; Aqualon RN20). The flask was heated to 80°C while being purged with nitrogen, and then 0.2 parts of ammonium persulfate was added. A pre-emulsion for dropping was prepared, consisting of 13.0 parts of butyl methacrylate, 10.5 parts of butyl acrylate, 1.2 parts of an 80% aqueous solution of acrylic acid, 11.0 parts of ion-exchanged water, 1.0 part of α-sulfonato-ω-(1-(allyloxymethyl)-alkyloxypolyoxyethylene)ammonium salt (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.; Aqualon KH10), and 0.5 parts of 2-polyoxyethylene-4-nonyl-2-propenylphenyl ether (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.; Aqualon RN20), and was added dropwise uniformly to the flask over 120 minutes. After the dropwise addition was completed, the contents of the flask were maintained at 80°C for 60 minutes. Subsequently, while maintaining the temperature in the flask at 80°C, a pre-emulsion for dropping was prepared, consisting of 3.5 parts butyl acrylate, 21.0 parts methyl methacrylate, 0.5 parts 3-methacryloxypropyltrimethoxysilane (Shin-Etsu Silicone KBM503), 0.5 parts 3-glycidoxypropyltrimethoxysilane (Shin-Etsu Silicone KBM403), 10.0 parts ion-exchanged water, 0.2 parts α-sulfonato-ω-(1-(allyloxymethyl)-alkyloxypolyoxyethylene)ammonium salt (Dai-ichi Kogyo Seiyaku Co., Ltd.; Aqualon KH10), and 0.1 parts 2-polyoxyethylene-4-nonyl-2-propenylphenyl ether (Dai-ichi Kogyo Seiyaku Co., Ltd.; Aqualon RN20). This pre-emulsion was added dropwise to the flask uniformly over 120 minutes. After the dropwise addition was completed, the mixture was further aged for 120 minutes with continued stirring. The mixture was cooled to room temperature and adjusted to a solids content of 50% and a pH of 8.5 to obtain Acrylic Emulsion C. The glass transition temperatures of the first-stage emulsion particles contained in the resin emulsion obtained above were 15.2°C, the second-stage emulsion particles were 70.1°C, and the entire emulsion particles were 40.6°C.Furthermore, since acrylic emulsion C contains a crosslinked structure, the molecular weight could not be measured.

[0103] <Acrylic Emulsion D> A flask equipped with a stirrer, reflux condenser, thermometer, dropping device, and nitrogen inlet tube was charged with 31.0 parts of ion-exchanged water, 0.5 parts of α-sulfonato-ω-(1-(allyloxymethyl)-alkyloxypolyoxyethylene)ammonium salt (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.; Aqualon KH10), and 0.2 parts of 2-polyoxyethylene-4-nonyl-2-propenylphenyl ether (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.; Aqualon RN20). The flask was heated to 80°C while being purged with nitrogen, and then 0.2 parts of ammonium persulfate was added, followed by the addition of methyl methacrylate. A pre-emulsion for dropping was prepared from the monomers: 24.0 parts of acrylic acid, 9.0 parts of butyl acrylate, 15.5 parts of styrene, 1.2 parts of an 80% aqueous solution of acrylic acid, 21.0 parts of ion-exchanged water, 1.5 parts of α-sulfonato-ω-(1-(allyloxymethyl)-alkyloxypolyoxyethylene)ammonium salt (Dai-ichi Kogyo Seiyaku Co., Ltd.; Aqualon KH10), and 1.0 part of 2-polyoxyethylene-4-nonyl-2-propenylphenyl ether (Dai-ichi Kogyo Seiyaku Co., Ltd.; Aqualon RN20). This pre-emulsion was added dropwise to the flask over 120 minutes. After the dropwise addition, the mixture was aged for another 120 minutes with continued stirring. The mixture was cooled to room temperature and adjusted to a solids content of 50% and a pH of 8.5 to obtain Acrylic Emulsion D. The glass transition temperature of the resulting Acrylic Emulsion D was 59.7°C. The weight-average molecular weight of Acrylic Emulsion D measured using GPC was greater than 100,000.

[0104] <Acrylic Emulsion E> A flask equipped with a stirrer, reflux condenser, thermometer, dropping device, and nitrogen inlet tube was charged with 31.0 parts of ion-exchanged water, 0.5 parts of α-sulfonato-ω-(1-(allyloxymethyl)-alkyloxypolyoxyethylene)ammonium salt (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.; Aqualon KH10), and 0.2 parts of polyoxyalkylene alkyl ether (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.; Noigen ET-170). The flask was heated to 80°C while being purged with nitrogen, and then persulfate was added. 0.2 parts of ammonium was added, and a pre-emulsion for dropping was prepared, consisting of monomers: 9.0 parts of styrene, 10.5 parts of methyl methacrylate, 2.0 parts of butyl acrylate, 0.5 parts of an 80% aqueous solution of acrylic acid, 11.0 parts of ion-exchanged water, and 0.5 parts of α-sulfonato-ω-(1-(allyloxymethyl)-alkyloxypolyoxyethylene)ammonium salt (Aqualon KH10, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), and this pre-emulsion was added dropwise uniformly into the flask over 120 minutes. After the dropwise addition was completed, the contents of the flask were maintained at 80°C for 60 minutes. Subsequently, while maintaining the temperature in the flask at 80°C, a pre-emulsion for addition consisting of the following monomers was prepared: 6.0 parts styrene, 12.5 parts butyl acrylate, 2.5 parts methyl methacrylate, 0.5 parts 80% aqueous acrylic acid solution, 1.0 parts diacetone acrylamide, 11.0 parts ion-exchanged water, and 0.5 parts α-sulfonato-ω-(1-(allyloxymethyl)-alkyloxypolyoxyethylene)ammonium salt (Aqualon KH10, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.). This pre-emulsion was added dropwise to the flask uniformly over 120 minutes. After the dropwise addition was completed, the mixture was further aged for 120 minutes with continued stirring. The mixture was cooled to room temperature and adjusted to a solids content of 46% and a pH of 9.0 to obtain Acrylic Emulsion E. The glass transition temperature of the first-stage emulsion particles contained in the resin emulsion obtained above was 80.1°C, the glass transition temperature of the second-stage emulsion particles was -5.3°C, and the glass transition temperature of the entire emulsion particles was 31.5°C. Furthermore, since Acrylic Emulsion E contains a crosslinked structure, the molecular weight could not be measured.

[0105] <Synthesis of water-based resin> <Acrylic Dispersion A> A reactor equipped with a stirrer, thermometer, reflux condenser, dropping device, and nitrogen inlet tube was charged with 10 parts of methyl ethyl ketone, and the temperature was raised to 90°C while the atmosphere inside the reactor was replaced with nitrogen. Subsequently, a mixture B-1 containing 0.3 parts of 2,4-diphenyl-4-methyl-1-pentene (NOF Corporation; Nofmer MSD), 7.9 parts of styrene, 3.9 parts of methyl methacrylate, 6.8 parts of tert-butyl methacrylate, 6.4 parts of n-butyl acrylate, 1.0 part of 2-hydroxyethyl methacrylate, and 0.3 parts of tert-butyl peroxy-2-ethylhexanoate (polymerization initiator), which had been previously mixed and stirred in a separate container, was added dropwise over 3 hours. After the dropwise addition was completed, a mixture of 0.3 parts of tert-butyl peroxy-2-ethylhexanoate (polymerization initiator) and 1.0 parts of methyl ethyl ketone, which had been previously mixed and stirred in a separate container, was added dropwise over 1 hour while maintaining the same temperature. The resulting mixture was allowed to react for 6 hours while maintaining the same temperature, after which 0.5 parts of 2-methacryloyloxyethyl isocyanate and 1.0 parts of methyl ethyl ketone were added, and stirring was continued for another 2 hours. Subsequently, a mixture B-2 of 1.3 parts of styrene, 3.9 parts of methyl methacrylate, 1.3 parts of n-butyl acrylate, 2.0 parts of methacrylic acid, and 0.2 parts of tert-butyl peroxy-2-ethylhexanoate (polymerization initiator), which had been previously mixed and stirred in a separate container, was added dropwise over 1 hour. After the dropwise addition was completed, a mixture of 0.2 parts tert-butyl peroxy-2-ethylhexanoate (polymerization initiator) and 1.0 parts methyl ethyl ketone, which had been previously mixed and stirred in a separate container, was added dropwise over 1 hour while maintaining the same temperature. The resulting mixture was stirred for 6 hours while maintaining the same temperature, and then cooled. 2.3 parts triethylamine was added to the resulting mixture and stirred, followed by the addition of 47.86 parts ion-exchanged water. From this mixture, 12 parts methyl ethyl ketone was distilled off under reduced pressure (approximately 50 mmHg) at 50°C using an evaporator. Subsequently, 7.5 parts ion-exchanged water, 5.0 parts ethylene glycol mono-n-butyl ether, 0.02 parts antifoaming agent, and 0.02 parts preservative were added to obtain Acrylic Dispersion B with a heating residue of 35%.The resin contained in Acrylic Dispersion B had a glass transition temperature Tg of 50°C and a weight average molecular weight of 37,000.

[0106] <Acrylic Dispersion B> A reactor equipped with a stirrer, thermometer, reflux condenser, dropping device, and nitrogen inlet tube was charged with 10 parts of methyl ethyl ketone, and the temperature was raised to 90 °C while the inside of the reactor was purged with nitrogen. Subsequently, a mixture B-1 consisting of 0.3 parts of 2,4-diphenyl-4-methyl-1-pentene (NOF Corporation; Nofmer MSD), 7.9 parts of styrene, 7.9 parts of methyl methacrylate, 9.2 parts of n-butyl acrylate, 1 part of 2-hydroxyethyl methacrylate, and 0.3 parts of tert-butyl peroxy-2-ethylhexanoate (polymerization initiator), which had been previously mixed and stirred in a separate container, was added dropwise over 3 hours. After the addition was completed, the same temperature was maintained, and a mixture of 0.3 parts of tert-butyl peroxy-2-ethylhexanoate (polymerization initiator) and 1 part of methyl ethyl ketone, which had previously been mixed and stirred in a separate container, was added dropwise over 1 hour. The resulting mixture was stirred for 6 hours while maintaining the same temperature, and then allowed to react. Then, 0.5 parts of 2-methacryloyloxyethyl isocyanate and 1 part of methyl ethyl ketone were added, and stirring was continued for another 2 hours. Subsequently, a mixture B-2 consisting of 1.3 parts of styrene, 1.3 parts of methyl methacrylate, 3.9 parts of n-butyl acrylate, 2 parts of methacrylic acid, and 0.2 parts of tert-butyl peroxy-2-ethylhexanoate (polymerization initiator), which had been previously mixed and stirred in a separate container, was added dropwise over 1 hour. After the addition was complete, a mixture of 0.2 parts of tert-butyl peroxy-2-ethylhexanoate (polymerization initiator) and 1 part of methyl ethyl ketone, which had been previously mixed and stirred in a separate container, was added dropwise over 1 hour while maintaining the same temperature. The resulting mixture was stirred for 6 hours while maintaining the same temperature, and then cooled. To the resulting mixture, 2.3 parts of triethylamine was added and stirred, and 47.86 parts of ion-exchanged water was further added. From this, 12 parts of methyl ethyl ketone was distilled off using an evaporator under reduced pressure (approximately 50 mmHg) at 50°C, and then 7.5 parts of ion-exchanged water, 5 parts of ethylene glycol mono-n-butyl ether, 0.02 parts of antifoaming agent, and 0.02 parts of preservative were added to obtain Acrylic Dispersion B with a heating residue of 35%. The resin contained in Acrylic Dispersion B had a glass transition temperature Tg of 21°C and a weight-average molecular weight of 40,000.

[0107] <Urethane dispersion> A glass round-bottom flask equipped with a stirrer, thermometer, nitrogen inlet, and condenser was charged with 261 parts of ETERNACOLL UH-200 (registered trademark; Ube Industries, Ltd. polycarbonate diol; number average molecular weight 2000; hydroxyl value 56.1 mg KOH / g; polycarbonate diol obtained by reacting 1,6-hexanediol and dimethyl carbonate), 17.5 parts of 2,2-dimethylolpropionic acid (DMPA), and 166 parts of N-methylpyrrolidone (NMP) under a nitrogen stream. 115 parts of 4,4'-dicyclohexylmethane diisocyanate (hydrogenated MDI) and 0.3 parts of dibutyltin dilaurate (catalyst) were added, heated to 90°C, and stirred for 5 hours to obtain a polyurethane prepolymer. The free NCO group content at the end of the urethanization reaction was 2.50%. 13.3 parts of triethylamine was added to the reaction mixture and mixed, and 512 parts of the mixture was withdrawn and added to 850 parts of water under vigorous stirring. Next, 33.6 parts of a 35% aqueous solution of 2-methyl-1,5-pentanediamine (MPMD) was added to carry out a chain extension reaction, and 22.3 parts of a 35% aqueous solution of butylamine (BA) was added to carry out a molecular end-capping reaction, yielding a polyurethane dispersion with a heating residue of 35%. The resulting polyurethane dispersion had a glass transition temperature (Tg) of 30°C and a weight-average molecular weight of 40,000.

[0108] <Epoxy Dispersion A> A reactor equipped with a stirrer, condenser, thermometer, and nitrogen gas inlet tube was charged with 125 parts of methyl ethyl ketone, 210 parts of bisphenol A epoxy resin (Epotohto YD-014, manufactured by Tohto Kasei Co., Ltd., epoxy equivalent weight 950), and 75 parts of polyethylene glycol diglycidyl ether (Denacol EX-841, manufactured by Nagase Chemical Industries, Ltd.). The mixture was dissolved at 100°C under a nitrogen stream. Then, 22.0 parts of octylamine and 14.7 parts of dibutylamine were added and reacted for 5 hours to obtain a modified epoxy resin. A mixture of 16.0 parts of acrylic acid, 10.0 parts of styrene, 10.0 parts of butyl acrylate, 40.0 parts of methyl ethyl ketone, and 12.0 parts of tert-butylperoxy-2-ethylhexanoate was then added dropwise over 1 hour and the mixture was incubated for 4 hours. After cooling to 80°C, 21.0 parts of triethylamine and 500 parts of water were added in that order and mixed to obtain an aqueous dispersion. The solvent was then removed and the nonvolatile content was adjusted to 37.0% with water to obtain Epoxy Dispersion A with a pH of 9.7, a weight average molecular weight of 20,000, a solid acid value of 31, and a glass transition temperature of 55°C.

[0109] <Epoxy Dispersion B> A nitrogen-purged four-neck flask was charged with 120 parts of n-butanol and 150 parts of bisphenol A-type epoxy resin (Epikote 1010, manufactured by Yuka Shell Epoxy Co., Ltd., epoxy equivalent weight 3000-5000) and heated to dissolve. A homogeneous mixture of raw materials (25 parts of methacrylic acid, 11 parts of styrene, 1.0 part of ethyl acrylate, 3.0 parts of benzoyl peroxide, and 10 parts of n-butanol) was gradually added dropwise to the solution over a period of 2 hours while stirring and maintaining the flask at 110°C. After the addition, the mixture was stirred at the same temperature for another 4 hours to obtain a carboxyl group-containing self-emulsifying vinyl polymer-modified epoxy resin solution with a solids content of 58%. Next, 100 parts of the carboxyl group-containing self-emulsifying epoxy resin solution was charged into a nitrogen-filled four-neck flask and heated to 100°C. A mixture of 4.0 parts of dimethylethanolamine and 260 parts of ion-exchanged water was added dropwise over 10 minutes with stirring to obtain an aqueous dispersion of the target resin. Further, 130 parts of n-butanol and water were removed by azeotropic distillation under reduced pressure to obtain Epoxy Dispersion B, a solvent-free target resin with a nonvolatile content of 25%. Epoxy Dispersion B had a glass transition temperature of 70°C and a weight-average molecular weight of 58,000.

[0110] <Water-soluble acrylic resin> A reactor equipped with a stirrer, thermometer, reflux condenser, dropping device, and nitrogen inlet tube was charged with 15 parts of methyl ethyl ketone, and the temperature was raised to 90 °C while the atmosphere inside the reactor was replaced with nitrogen. Subsequently, a mixture of 0.05 parts of 2,4-diphenyl-4-methyl-1-pentene (NOF Corporation; Nofmer MSD), 5.0 parts of styrene, 5.0 parts of methyl methacrylate, 13.0 parts of n-butyl acrylate, 8.3 parts of 2-hydroxyethyl methacrylate, 3.85 parts of methacrylic acid, and 0.3 parts of tert-butyl peroxy-2-ethylhexanoate (polymerization initiator), which had been previously mixed and stirred in a separate container, was added dropwise over 5 hours. After the addition was completed, the same temperature was maintained, and a mixture of 0.3 parts of tert-butyl peroxy-2-ethylhexanoate (polymerization initiator) and 2 parts of methyl ethyl ketone, which had been previously mixed and stirred in a separate container, was added dropwise over 1 hour. The resulting mixture was stirred for 6 hours while maintaining the same temperature, and then cooled. 4.5 parts of triethylamine was added to the resulting mixture and stirred, followed by the addition of 42.7 parts of ion-exchanged water. From this mixture, 15.0 parts of methyl ethyl ketone was distilled off at 50°C under reduced pressure (approximately 50 mmHg) using an evaporator. Next, 10 parts of ion-exchanged water, 5.0 parts of ethylene glycol mono-n-butyl ether, 0.02 parts of antifoaming agent, and 0.02 parts of preservative were added to prepare an aqueous acrylic resin solution with a heating residue of 35%, thereby synthesizing a water-soluble acrylic resin. The water-soluble acrylic resin contained in the aqueous acrylic resin solution had a glass transition temperature (Tg) of 22°C and a weight-average molecular weight (Mw) of 45,000.

[0111] *Glass transition temperature The glass transition temperatures (Tg) of the resins of the acrylic emulsions A to E, acrylic dispersions A and B, urethane dispersions, epoxy dispersions A and B, and aqueous acrylic resin solutions were calculated using the following FOX formula. [FOX formula] 1 / Tg=W1 / Tg1+W2 / Tg2+···+Wi / Tgi+···+Wn / Tgn In the FOX formula, Tg written in the denominator on the left side represents the glass transition temperature (unit: K) of the polymer component consisting of N types of monomers, Tg(1, 2, i, N) represents the glass transition temperature (unit: K) of each monomer, W(1, 2, i, N) is the mass fraction of each monomer, and the relationship W1 + W2 +··· + Wi +··· + Wn = 1 holds. Here, the glass transition temperature of a monomer means the glass transition temperature of its homopolymer.

[0112] *Weight average molecular weight The weight average molecular weight was measured by gel permeation chromatography (GPC), and a converted value obtained from a calibration curve of standard polystyrene prepared in advance was used.

[0113] <Preparation of water-based paint> Water-based paints were prepared using the prepared acrylic emulsions A to E, acrylic dispersions A and B, urethane dispersion, epoxy dispersions A and B, and acrylic resin aqueous solutions, by stirring the components according to the formulations shown in Tables 1 to 3 with a disperser. The amount of each component in the formulations shown in the tables is shown in parts by mass. Next, the drying property, blocking resistance, initial water resistance, and corrosion resistance of the water-based paint were evaluated. The results are shown in Tables 1 to 3. The evaluation methods will be described later.

[0114] [Table 1]

[0115] [Table 2]

[0116] [Table 3]

[0117] The pigments and dispersants shown in the table are described below. Extender pigment (precipitated barium sulfate): "Precipitated Barium 100", manufactured by Sakai Chemical Industry Co., Ltd. Anti-rust pigment (zinc phosphate): "K-WHITE #140W", manufactured by Teika Co., Ltd. Color pigment (titanium oxide): "R-32", manufactured by Sakai Chemical Industry Co., Ltd. Dispersant: "DISPERBYK-194N", manufactured by BYK Japan Co., Ltd.

[0118] The "heating residue (%)" in the table is synonymous with the amount (mass %) of the film-forming components in the water-based paint. "PVC" in the table is the pigment volume concentration, which is the ratio of the total volume of the pigment to the total volume of the film-forming components in the water-based paint.

[0119] The measurement method for the "spectrum peak in the temperature change curve of loss tangent (tan δ)" in the table is as follows. A mixture of resin components shown in the formulation in the table was applied to a polypropylene (PP) plate preheated to 80°C using an applicator so that the dry film thickness was 50 μm, and the plate was forcedly dried at 80°C for 30 minutes to obtain an isolated film made of the resin components of the formulation in the table. Using an RSA-GII (manufactured by TA Instruments), the loss modulus and storage modulus of the isolated film were measured at each temperature under the following measurement conditions. The loss tangent was calculated from the loss modulus and storage modulus, a temperature change curve of the loss tangent was created, and the spectral peak value of the loss tangent was read. <Measurement conditions> Temperature range: -50℃~200℃ Heating rate: 5℃ / min Measurement length: 24.0 mm Measurement width: 8.0 mm Frequency: 1Hz Distortion: 0.05%

[0120] The "crosslink density (mol / cc)" in the table is the crosslink density of the coating film obtained from the water-based paint, and is calculated using the formula n = E' / 3RT (where n is the crosslink density (mol / cc) of the coating film, E' is the plateau storage modulus (Pa) of the coating film at a frequency of 1 Hz, T is the absolute temperature (K) of the plateau storage modulus of the coating film, and R is the gas constant (8.31 x 10 6 The storage modulus of the coating film in the plateau region is measured as follows: The aqueous coating was applied to a polypropylene (PP) plate preheated to 80°C using an applicator so that the dry film thickness was 50 μm, and the plate was forcedly dried at 80°C for 30 minutes to obtain an isolated film. The storage modulus of the isolated film was measured using an RSA-GII (manufactured by TA Instruments) under the following measurement conditions, and the plateau region storage modulus of the coating film was read. <Measurement conditions> Temperature range: -50℃~200℃ Heating rate: 5℃ / min Measurement length: 24.0 mm Measurement width: 8.0 mm Frequency: 1Hz Distortion: 0.05%

[0121] The "softening point" in the table is the softening point of the coating film obtained from the water-based paint, and represents Tg1 (the temperature at which molecules begin to move) in viscoelasticity measurements. Details of the method for measuring the softening point of the coating film are as follows. The aqueous coating was applied to a polypropylene (PP) plate preheated to 80°C using an applicator so that the dry film thickness was 50 μm, and the plate was forcedly dried at 80°C for 30 minutes to obtain an isolated film. The storage modulus of the isolated film was measured using an RSA-GII (manufactured by TA Instruments) under the following measurement conditions, and the change point of the storage modulus (the temperature at which the decrease began) was read as Tg1, which was taken as the softening point. <Measurement conditions> Temperature range: -50℃~200℃ Heating rate: 5℃ / min Measurement length: 24.0 mm Measurement width: 8.0 mm Frequency: 1Hz Distortion: 0.05%

[0122] In the table, "Resin with a molecular weight of less than 100,000 (%)" indicates the proportion (mass %) of resin with a molecular weight of less than 100,000 in the total resin components shown in the compounding recipe in the table. In the table, "Resin with a molecular weight of 100,000 or more or with a crosslinked structure (%)" indicates the percentage (mass %) of resin with a molecular weight of 100,000 or more or resin with a crosslinked structure among all resin components shown in the formulation in the table.

[0123] Evaluation Method <Drying> A water-based paint was applied to a steel plate with a surface temperature maintained at 40°C ± 5°C so that the film thickness immediately after application was 100 μm, and the painted surface of the steel plate was then maintained at 40°C ± 5°C, and the surface drying property of the resulting paint film was evaluated in accordance with the test method (Balochni method) of JIS K 5600-3-2. The time required for the ballochni to be lightly brushed on and removed without scratching the surface of the paint film was taken as the surface drying time, and drying property was evaluated according to the following criteria. ◎: Surface drying time is less than 3 minutes ○: Surface drying time is between 3 and 5 minutes △: Surface drying time is between 5 and 10 minutes ×: Surface drying time is 10 minutes or more

[0124] <Blocking resistance> Two 100 x 100 x 0.3 mm tin plates with a surface temperature maintained at 80°C ± 5°C were coated with a water-based paint so that the film thickness immediately after coating was 100 μm, and then the plates were forced to dry at 100°C for 30 minutes to prepare test specimens. The two test specimens were stacked with the coated surfaces facing inwards, and a pressure of 20 kg (0.2 kg / cm) was applied evenly. 2 After placing a weight of 1.0g on the sample and maintaining the temperature at 40°C ± 5°C for 30 minutes, the weight was removed and the blocking resistance was evaluated based on the state of pressure bonding and peeling according to the following criteria. ◎: No pressure adhesion is observed and no marks remain on the coating surface. ○: Light pressure is observed, but no marks remain on the coating surface. △: Pressure adhesion was observed, and marks remained on the coating surface. ×: Pressure adhesion was observed and peeling was observed on the coating surface.

[0125] <Initial water resistance> Using an SS400 blast plate with a surface temperature maintained at 80°C ± 5°C, a water-based paint was applied so that the dry film thickness would be 100 μm, and then the plate was forced to dry at 100°C for 30 minutes.The lower half of the resulting test plate was then immersed in tap water at 23°C for 24 hours, and the appearance of the test plate was immediately observed after removal, and the initial water resistance was evaluated according to the following criteria. ⊚: There was no swelling in the coating film of the immersed area, and there was no visible difference in hue compared to the non-immersed area. ◯: There was no swelling in the coating film of the immersed area, but the difference in hue from the non-immersed area was clear. △: Partial swelling was observed in the coating film at the immersed area. ×: Blisters were observed throughout the entire coating film at the immersed area.

[0126] <Corrosion resistance> Using an SS400 blast plate with a surface temperature maintained at 80°C ± 5°C, a water-based paint was applied to a dry film thickness of 100 μm, followed by forced drying at 100°C for 30 minutes. Crosscuts were then made in the resulting coating to prepare test panels. The test panels were then sprayed with salt water for one week according to the method specified in JIS Z2371:2015. After testing, the test panels were evaluated based on the following criteria. The coating area without crosscuts was designated the general area, and the coating area with crosscuts was designated the cut area. ◎: No rust or swelling in the general area, and swelling in the cut area is only found less than 1 mm from the cut. ○: No rust or swelling in the general area, and swelling only occurs within 3 mm of the cut in the cut area. △: No rust or swelling in the general area, and swelling only occurs within 5 mm of the cut in the cut area. ×: Blisters have appeared in areas 5mm or more from the cut, and rust and blisters are found in the general areas.

Claims

1. A coating composition to be applied to a metal substrate, comprising water, an organic solvent, a pigment, and a resin, The pigment volume concentration (PVC) is in the range of 0.1 to 35%, the resin has at least one spectral peak in a temperature change curve of loss tangent (tan δ) measured at a measurement frequency of 1 Hz using a solid viscoelasticity measuring device based on JIS K7244-4, which is in the range of 45°C to 180°C; the resin contains resin particles having a heterogeneous phase structure, and the resin particles have at least two glass transition temperatures of less than 45°C and 55°C to 95°C; a coating film formed from the coating composition has two or more softening points, one of which is lower than 25°C and another of which is 45°C or higher; A coating composition characterized in that the pigment contains at least an anti-rust pigment and / or barium sulfate.

2. A coating composition to be applied to a metal substrate, comprising water, an organic solvent, a pigment, and a resin, The pigment volume concentration (PVC) is in the range of 0.1 to 35%, the resin has at least one spectral peak in a temperature change curve of loss tangent (tan δ) measured at a measurement frequency of 1 Hz using a solid viscoelasticity measuring device based on JIS K7244-4, which is in the range of 45°C to 180°C; The resin contains a resin having a molecular weight of less than 100,000 in a range of 1 to 30% by mass in the resin component, and a resin having a molecular weight of 100,000 or more or a resin having a crosslinked structure in a range of 20 to 99% by mass in the resin component, a coating film formed from the coating composition has two or more softening points, one of which is lower than 25°C and another of which is 45°C or higher; A coating composition characterized in that the pigment contains at least an anti-rust pigment and / or barium sulfate.

3. 3. A coating composition according to claim 1 or 2, characterized in that the pigment comprises zinc phosphate and / or barium sulfate.

4. 4. The coating composition according to claim 1, wherein the pigment volume concentration (PVC) is in the range of 5 to 35%.

5. 5. The coating composition according to claim 1, wherein the resin contains one or more monomers having an SP value in the range of 9.2 to 9.9 as constituent components, and the organic solvent contains one or more organic solvents having an SP value of 8.0 to 11.1 and a boiling point in the range of 160 to 260°C.

6. A coating film obtainable from the coating composition according to any one of claims 1 to 5, wherein the coating film is applied to a thickness of 100 µm on a preheated steel plate, and the surface drying time measured in accordance with JIS K 5600-3-2 (Barochini method) at a temperature of 35 to 45°C is 10 seconds to 5 minutes.

7. A coating composition described in any one of claims 1 to 5, characterized in that the minimum film formation temperature (MFT) of the coating composition is 5 to 25°C.

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